In Darwin’s time, the belief in the independent creation of species was mainstream, as was the belief that humans could not have been descended from animals.
In addition to his well-reasoned arguments (such as the occasional occurrence of zebra-stripes on young horses – he said that he’d almost as soon believe that God put seashells in the mountains to fool us, as believe that God put zebra stripes on non-zebras), he occasionally had a bit of fun.
Thus, in the second chapter of The Descent of Man, he writes:
“He who rejects with scorn the belief that the shape of his own canines, and their occasional great development in other men, are due to our early forefathers having been provided with these formidable weapons, will probably reveal, by sneering, the line of his descent. For though he no longer intends, nor has the power, to use these teeth as weapons, he will unconsciously retract his “snarling muscles” (thus named by Sir C. Bell), so as to expose them ready for action, like a dog prepared to fight.”